Many synthetic materials are presently used as surgical sutures. These materials may be used as single filament strands, i.e., monofilament sutures, or as multifilament strands in a braided, twisted or other multifilament construction. Synthetic sutures have been made from materials such as polypropylene, nylon, polyamide, polyethylene, polyesters such as polyethylene terephthalate, and segmented polyether-ester block copolymers. In addition, absorbable synthetic sutures have been prepared from synthetic polymers such as polymers containing glycolide, lactide, dioxanone and/or trimethylene carbonate.
Natural materials have also been used to make sutures. For example, silk has been used to make non-absorbable sutures. As another example, catgut sutures are absorbable sutures made from a natural material.
Sutures intended for the repair of body tissues must meet certain requirements: they must be non-toxic, capable of being readily sterilized, they must have good tensile strength and have acceptable knot-tying and knot characteristics.
The performance of a suture in terms of knot run down, knot security and tissue drag are particularly important to surgeons. Knot run down performance, which reflects the ease of placement of a knot tied in a suture, is important in surgical procedures where it is necessary that a knot be tied in a suture when the knot is deep inside a surgical or natural opening. For instance, a dental surgeon may need to tie a knot inside a patient's mouth. An intravaginal hysterectomy requires suturing in restricted quarters. One technique frequently used is to tie a square knot that can be run down from an exterior location where the knot is first tied to lie against tissue with a desired degree of tightness. The knot is snugged down so that it is holding with a degree of firmness chosen by the surgeon for a particular situation and then additional throws are tied down against the first throws of the square knot. In some instances, the first throw is a double twist followed by a single throw to form a surgeons' knot, with additional throws to form additional square knots on top as needed. The ease with which a knot runs down the suture depends on a number of factors such as composition of the suture, braid structure of the suture, and the nature of the coating, if any, applied to the suture. Preferably, the knot runs down the suture smoothly and easily.
Knot security is the ability of the knot to hold without slipping for an acceptable length of time. The characteristics of the suture material which allow a knot to hold securely are somewhat at odds with the characteristics of the suture material which provide satisfactory knot run down performance, since knot security requires that the suture grab itself while knot run down requires that the suture pass smoothly over itself. Accordingly, a balance of these two characteristics is normally required.
It is also desirable for a suture to have low tissue drag, which is a measure of the force required to pull a suture through tissue. High drag forces results in chatter as the suture passes through tissue, makes it more difficult for the surgeon to align tissue neatly, and increases the time to complete the closure being made with the suture.
A wide variety of coatings have been applied to sutures of various types to improve one or more characteristics of the suture. See, for example, U.S. Pat. Nos. 3,187,752; 3,527,650; 3,942,523; 4,105,304; and 4,185,637.
U.S. Pat. No. 3,187,752 describes non-absorbable silicone coated sutures, but does not describe the copolymers employed in the present invention or the superior results which are achieved by using those copolymers.
Fibers or textile treatments which include organo silicon compounds have been described in, inter alia, U.S. Pat. Nos. 3,280,160; 3,418,354; 4,283,519; 4,359,545; 4,217,228; 4,784,665; 3,837,891; 4,207,071; 4,184,004; 4,578,116; 4,937,277; 4,617,340; and 4,624,676.
Siloxane-oxyalkylene copolymers have been described in U.S. Pat. Nos. 3,629,310; 3,755,399; 3,280,160; 3,541,127; and 4,699,967. U.S. Pat. No. 4,043,344 describes non-absorbable sutures coated with polyoxyethylene-polyoxypropylene copolymer lubricant.